This invention relates to magnetic tape cassettes, and more particularly to an improvement of a so-called "Phillips" type magnetic tape cassette in which a magnetic tape is wound on a pair of hubs.
In general, in a magnetic tape cassette used for audio devices or the like, a pair of hubs on which a magnetic tape is wound are arranged in a cassette case made up of the upper and lower half cases. The magnetic tape is laid against right and left guide rollers arranged in the front part of the cassette so that the magnetic tape may be run through the front opening of the cassette.
Each of the guide rollers is rotatably provided in the cassette, and the magnetic tape is partially wound around each guide roller. Thus, when the guide rollers are rotated, one guide roller smoothly changes the direction of movement of the magnetic tape toward the recording and reproducing region in the front part of the cassette and the other guide roller smoothly changes the direction of movement of the magnetic tape toward the hub incorporating region. Accordingly, during a recording or reproducing operation, the tape running characteristic is greatly affected by the performance of rotation of the guide rollers. Especially in a magnetic tape cassette in which the guide rollers are rotatably mounted on guide roller supporting shafts which are extended from the lower half case, the performance of the guide rollers suffers from the following difficulty.
In general, in order to prevent the negative effects due to shrinkage which occurs in molding the half cases, an annular seat is formed in such a manner as to surround the base part of the supporting shaft. However, the lubrication between the upper end face of the seat and the roller end face is insufficient; therefore, the guide roller cannot turn smoothly, thus producing squeaks sometimes. If the guide roller is rotated for a long period under the condition which produces squeaks as described above, the aforementioned two end faces become worn. As a result, the guide roller is able to move up and down, which considerably decreases the smoothness of the tape running characteristic.
In the case where the above-described guide rollers are employed for a magnetic tape cassette, such as that operated in a digital system, which is higher in recording or reproducing density than a conventional audio magnetic tape cassette, the above-described difficulty is especially serious because the number of recording or reproducing tracks is large.